Japanese encephalitis (JE) is a viral disease caused by the Japanese encephalitis virus (JEV), a mosquito-borne flavivirus. It is primarily found in East and Southeast Asia, with sporadic cases reported in other regions. This paper provides a comprehensive overview of the epidemiology of Japanese encephalitis.
Historically, the first major outbreak of Japanese encephalitis was reported in Japan in the 1870s. In the 1920s, the virus was isolated for the first time, and its connection to neurological symptoms was established. Since then, JE has been recognized as a significant public health concern in many Asian countries.
Japanese encephalitis is endemic in 24 countries in the Asia-Pacific region, including India, China, Bangladesh, Vietnam, Thailand, Myanmar, and others. However, the disease can also spread to non-endemic regions, such as Australia, Papua New Guinea, and the Pacific Islands. Travelers from non-endemic regions can acquire the infection while visiting endemic areas.
JEV is mainly transmitted through the bite of infected mosquitoes, primarily from the Culex genus. Pigs and wading birds act as hosts for the virus, while mosquitoes serve as vectors for transmission between these animals and humans. JE is primarily a rural agricultural disease, common in areas with wetland rice cultivation and pig farming.
Children, especially those under 15 years of age, are the most affected population group by JE. However, adults who have not been previously exposed to the virus are also at risk. The disease is more prevalent in rural areas with abundant vector mosquitoes and amplifying hosts. Individuals involved in farming, rice field work, and those living near pig farms or wetlands are at a higher risk of JE.
According to the World Health Organization (WHO), approximately 68,000 cases of Japanese encephalitis occur annually, resulting in 13,600 to 20,400 deaths worldwide. However, these numbers are likely underestimated due to limited healthcare access and surveillance systems in affected regions. The case fatality rate varies widely, ranging from 5% to 30%, with higher rates in older populations.
Several risk factors increase the transmission of Japanese encephalitis:
1. Mosquito Exposure: Living or working in areas with high mosquito populations, especially during peak transmission seasons, increases the risk of JE.
2. Rural Agricultural Activities: People involved in rice farming and pig rearing are at an elevated risk due to close proximity to mosquito vectors and amplifying hosts.
3. Lack of Vaccination: Individuals who have not been previously vaccinated against JE are more susceptible to infection.
4. Travel to Endemic Areas: Travelers from non-endemic regions who visit areas with ongoing JE transmission are at risk if they are not immunized or take preventive measures to avoid mosquito bites.
The impact of Japanese encephalitis varies across different regions and populations. In endemic areas, particularly in rural and agricultural communities, the disease is a significant public health concern. Countries with high burden, such as India and China, report a substantial number of cases each year. Japanese encephalitis can cause long-term neurological disabilities, cognitive impairments, and economic burdens on affected individuals and their families.
Efforts have been made in recent years to control Japanese encephalitis through vaccination campaigns. Vaccination programs targeting high-risk populations, especially children in endemic areas, have shown promising results in reducing the disease burden.
In conclusion, Japanese encephalitis is a viral disease primarily found in Asia. It is transmitted through the bite of infected mosquitoes and primarily affects children and individuals living in rural agricultural areas. The disease has a significant impact on affected regions and populations, leading to substantial morbidity and mortality. Vaccination and control measures play a vital role in preventing the transmission and reducing the burden of Japanese encephalitis.

Download Data(下载数据)

Seasonal Patterns: Japanese encephalitis cases in mainland China exhibit a distinct seasonal pattern, characterized by a peak in activity during the summer months and reduced activity in the winter months. The number of cases starts to rise in May, reaches its peak in August, and gradually declines until December. From January to April, the number of cases remains generally low.
Peak and Trough Periods: The peak period for Japanese encephalitis cases in mainland China occurs in July and August. During these months, there is a significant increase in the number of cases, with July reporting the highest number of cases. The trough period for cases takes place from January to April, during which the number of cases is comparatively low compared to the rest of the year.
Overall Trends: Generally, the number of Japanese encephalitis cases in mainland China has displayed fluctuations over the years. There is variation in the number of cases from year to year, with certain years witnessing higher or lower numbers of cases. Nevertheless, there is a noticeable upward trend in recent years, peaking in 2011, 2012, and 2017. Following 2017, there has been a gradual decline in the number of cases.
Discussion: The seasonal patterns observed for Japanese encephalitis cases in mainland China align with the known biology and transmission dynamics of the disease. The primary mode of transmission is through mosquito bites, and the heightened mosquito activity during the warm summer months likely contributes to the increased number of cases during this time. The trough period from January to April can be attributed to reduced mosquito activity and diminished transmission.
The concerning trend of increasing cases in recent years could be influenced by various factors. Changes in climate and land usage, as well as population movement and urbanization, may contribute to the spread and persistence of the disease. Mitigation efforts, such as mosquito population control measures and vaccination administration, can help alleviate the impact of Japanese encephalitis in mainland China.
Close monitoring of the epidemiological patterns of Japanese encephalitis by public health authorities is crucial. Implementation of targeted interventions, including the promotion of mosquito control measures, ensuring access to vaccinations, and public education on prevention strategies, is essential in reducing the disease burden. Moreover, continuous surveillance and research on the factors influencing virus transmission and spread are critical for effective prevention and control efforts.